Silicon-oxygen-nitrogen layers for semiconductor devices

ABSTRACT

A protective layer for use in the manufacture of semiconductor devices and circuits and for thereafter protecting and passivating the devices comprising a combination of silicon, oxygen and nitrogen in selected atomic proportions.

United States Patent [191 Hall SlLlCON-OXYGEN-NITROGEN LAYERS FORSEMICONDUCTOR DEVICES U.S. Cl. 357/73; 357/54; 106/39; 106/52; 117/215Int. Cl H01] 5/00; H011 3/00 Field of Search 357/73, 54; 106/39, 52;117/215 References Cited UNITED STATES PATENTS 3,755,720 8/1973 Kern357/73 51 May 13, 1975 3,756,876 9/1973 Brownetal. ..3s7/54 PrimaryExaminer-Andrew J. James Attorney, Agent, or FirmFlehr, l-lohbach, Test,Albritton & Herbert [57] ABSTRACT A protective layer for use in themanufacture of semiconductor devices and circuits and for thereafterprotecting and passivating the devices comprising a combination ofsilicon, oxygen and nitrogen in selected atomic proportions.

5 Claims, 14 Drawing Figures SILICON-OXYGEN-NITROGEN LAYERS FORSEMICONDUCTOR DEVICES BACKGROUND OF THE INVENTION This invention relatesgenerally to masking, passivating and insulatingfilms or layers forsemiconductor devices and circuits and more particularly to siliconoxynitride films or layers.

Masking layers are generally applied to the surface of semiconductorwafers and selectively removed during the processing of the wafer toform devices, to thereafter support the interconnect metal layers and toprotect and passivate the devices. Silicon dioxide has been extensivelyused for this purpose. The oxide layer serves to mask and insulate andpassivate junctions which extend to the surface. More recently, silicondioxide insulating layers have been used in metal-oxide silicon (MOS)structures for masking, insulating and junction protection.

Silicon dioxide layers have several drawbacks. Grown or depositedsilicon dioxide layers on a silicon substrate are generally undercompressive stresses giving rise to high recombination currents at thesurface thereby increasing leakage across the junction. Silicon oxidedoes not effectively mask against alkaline metal atoms, such as sodiumatoms. Consequently, they diffuse through the layer and introduceinstabilities where the PN junction intersects the surface of thedevice.

It has been suggested that layers of silicon nitride can be used forprotection against migration of impurities which deleteriously affectthe operation of the devices. However, such protective layers introducelarge tensile stresses giving rise to high recombination currents at thesurface with silicon dioxide. It has been suggested that the protectiveor insulating film can be a composition of silicon, oxygen and nitrogen.

OBJECTS AND SUMMARY OF INVENTION It is a general object of the presentinvention to provide an improved masking, insulating, protective andpassivating layer comprising a selected combination of silicon, oxygenand nitrogen, for semiconductor devices.

It is another object of the present invention to provide siliconoxynitride protective films that can be grown and processed usingprocesses similar to those used for silicon dioxide whereby devices suchas bipolar, MOS, MOS/LSI, integrated circuits and the like can befabricated using substantially conventional techniques for the masking,etching, diffusion, metallizing and other processing steps.

The foregoing objects are achieved by providing a protective layercomprising silicon oxynitride (Si 0,, N where x, y and z are atomicpercentages respectively for Si, O, and N, and are selected to provide aprotective layer which minimizes stress between the device body and thelayer and which inhibits the diffusion of impurity atoms through thelayer, particularly alkaline metal atoms, such as sodium. Moreparticularly, the device includes a silicon oxynitride film in which xis between 30 and 40%; y between 45 and 55%; and z between and 20%.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A-1G show the steps ofmanufacturing a metal-oxide-silicon (MOS) device in accordance with theinvention.

FIG. 2 is a plan view ofthe device of FIG. 1G showing the metalinterconnections overlying the silicon DESCRIPTION OF PREFERREDEMBODIMENT The use of the improved layer for masking, protecting andpassivating silicon semiconductor is first described in connection withthe manufacture of a metaloxide-silicon field effect transistor(MOSFET). Referring to FIGS. lA-lG, a silicon substrate 11 of n-type orp-type conductivity and with selected impurity concentration, FIG. 1A,is treated to form thereon an insulating masking layer 12 ofsilicon-oxygen-nitrogen (Si 0,, N The layer 12 may be formed byintroducing a silane gas, nitrogen hydride gas and oxygen (Si H, NH,, 0into a chamber or oven held at an elevated temperature of 750C 1100C inwhich the substrate is placed. The gases interact and deposit Si I O,,N, layer 12 on the surface by vapor deposition, FIG. 13. By introducinga selected volume ratio of silane, nitrogen hydride and oxygen, it ispossible to deposit a layer having selected atomic ratio. In accordancewith the invention, the atomic ratio is selected so that the layer isadherent to the surface of the substrate, so that it has substantiallythe same coefficient of expansion as the substrate, so that itpassivates the PN junction extending to the surface so that it masksagainst the migration of alkaline earth metal atoms and so that it canbe etched. By masking and etching using conventional masking techniquesand etching with conventional buffered etching solutions such as abuffered I-IF solution, portions of the layer 12 are removed to formspaced windows 13 and 14, FIG. 1C. Thereafter, regions 16 and 17, ofopposite conductivity type, are formed by diffusion or ion implantation,FIG. 1D. A new Si, 0,, N, layer 18 is grown to cover the surface, FIG.1B. The layer may be formed by vapor deposition during the diffusionprocess. The wafer is then again masked and etched to form windows 21and 22. A metal layer 23 is then provided on the surface and extendinginto the windows to contact the underlying regions 16 and 17, FIG. 1F.The layer is then selectively etched to form source contact 26, draincontact 27 and gate contact 28, FIGS. 16 and 2.

In accordance with the invention, the composition of thes'ilicon-oxygen-nitrogen (Si, 0,, N masking layer 12 in which x, y and zare the atomic percentages respectively for silicon, oxygen and nitrogenis as follows:

Layers having the foregoing atomic percentage s have been found to bereadily etched by standard etches such as buffered I-IF, have been foundto be impervious to the migration of sodium, have minimum stress withthe underlying silicon, have a minimum of recombination currents at thejunction thereby passivating the junction and serve to suitably supportmetal layers forming the interconnections for the devices formed in awafer. It is further noted that the above processes are readilyadaptable to the conventional processing steps protecting andpassivating layer in accordance with the invention is shown in FIGS.3A-3F wherein the insulating layer in accordance with the invention isillustrated for the formation of a bipolar transistor. Moreparticularly, a silicon substrate 31 of n-type conductivity withselected impurity concentration is processed as described above to formthereon a silicon-oxygennitrogen insulating layer 32 in accordance withthe present invention which is masked and etched by conventionaltechniques to form window 33. The layer 32 may be formed as describedabove, that is, by chemical vapor deposition. An impurity of oppositeconductivity type is then deposited on the exposed surface of thesilicon at the window 33 and thereafter the layer is diffused into thesilicon body to form a region 34 which forms junction 35 with the wafer31. The junction 35 extends to the surface beneath the surface layer 33.The diffusion is carried out in a suitable atmosphere whereby toredeposit a silicon-oxygen-nitrogen layer 36 on the surface, FIG. 3B.The device of FIG. 3B is then suitably masked and etched to form spacedwindows 37 and 38, FIG. 3C.

The device is then deposited with an impurity of the same conductivitytype and suitably diffused to form spaced diffused regions 41 and 42,FIG. 3D. It is to be noted that the ends of the junctions 43 and 35extend to the surface beneath the layer 32. Thereafter, spaced windows46, 47 and 48 are opened to provide means for making ohmic contact withthe various layers, FIG. 3E. A metal layer is applied to the surface byevaporation or sputtering to extend into the windows to contact theexposed regions. The metal layer is thereafter etched to form thecollector, base and emitter contacts. The buried region 41 forms a goodohmic connection with the collector region, while the metal layerscontact the emitter and base directly; the contacts to the emitter, baseand collectors are identified by the letters e, b and 0, FIG. 3F.

Thus, it is seen that the process lends itself to the formation ofbipolar as well as unipolar devices such as the device shown in FIG. 1and is readily adaptable to all types of integrated circuitapplications.

In all instances, the junctions are protected and passivated by thesilicon-oxygen-nitrogen (Si 0,, N,,) layer which has minimumrecombination currents at the junction which suitably masks againstsodium ion migration in that it is substantially impervious to thesodium ion migration. The protective layer further reduces stresses inthat it has substantially the same coefficient of expansion as theunderlying silicon layer. During the processing of the device, the layersuitably serves as a mask which is readily processed by conventionaltechniques.

I claim:

1. In a semiconductor device of the type which includes a substrate ofsemiconductor material of one conductivity type and a region of oppositeconductivity type extending therein and to form a junction therewithwhich extends to one surface of the device, a protective layer carriedon said one surface of the device and extending over said junction topassivate and protect the junction, said layer comprising a compositionof silicon, oxygen and nitrogen (Si 0,, N in which x 30% to 40% y 45% to55% z 10% to 20% where z, y and'z are the atomic percentages forsilicon, oxygen and nitrogen respectively.

2. A semiconductor device as in claim 1 wherein the substrate issilicon.

3. A semiconductor device as in claim 2 wherein said protectiveinsulating layer includes a window over said region of oppositeconductivity type and a metal layer overlies a portion of said layer andextends into said window to form ohmic contact with said region.

4. A semiconductor device including a silicon substrate of oneconductivity type, spaced regions of opposite conductivity typeextending into said substrate and forming junctions therewith, aprotective and insulating layer formed on one surface of said device andextending over said junctions, said layer comprising a composition ofsilicon, oxygen and nitrogen (Si, 0,, N in which a x 30% to 40% y 45% to55% z 10% to 20% where x, y and z are the atomic percentages forsilicon, oxygen and nitrogen respectively, spaced openings formed insaid layer over said regions, metal layers extending over saidinsulating layer and extending to said regions to make ohmic contacttherewith, and an additional metal layer over the portion of theinsulating layer between said regions, said metal layers forming sourceand drain contacts and said additional metal layer forming the gatecontact of a metal oxide silicon field effect transistor.

5. A semiconductor device including a silicon substrate of oneconductivity type, a region of opposite conductivity type extending intosaid substrate to form a junction therewith, spaced regions of the sameconductivity type extending into said substrate, one of said regionsextending into said region of opposite conductivity type to form ajunction therewith, a protective insulating layer carried on said onesurface extending over said junction to passivate and protect thejunction, said layer comprising a composition of silicon, oxygen andnitrogen (Si 0,, N in which x 30% to 40% y 45% to 55% z 10% to 20% wherex, y and z are the atomic percentages for silicon, oxygen and nitrogenrespectively, openings formed in said layer to expose said region ofopposite conductivity type and said spaced regions of the sameconductivity type, a metal layer having individual portions extendinginto said openings to contact said regions and carried by the insulatinglayer, said individual portions defining emitter, base and collectorcontacts.

1. IN A SEMICONDUCTOR DEVICE OF THE TYPE WHICH INCLUDES A SUBSTRATE OFSEMICONDUCTOR MATERIAL OF ONE CONDUCTIVITY TYPE AND A REGION OF OPPOSITECONDUCTIVITY TYPE EXTENDING THEREIN AND TO FORM A JUNCTION THERWITHWHICH EXTENDS TO ONE SURFACE OF THE DEVICE, A PROTECTIVE LAYER CARRIEDON SAID ONE SURFACE OF THE DEVICE AND EXTENDING OVER SAID JUNCTION TOPASSIVATE AND PROTECT THE JUNCTION, SAID LAYER COMPRISING A COMPOSITIONOF SILICON, OXYGEN AND NITROGEN (SIX OV NZ) IN WHICH
 2. A semiconductordevice as in claim 1 wherein the substrate is silicon.
 3. Asemiconductor device as in claim 2 wherein said protective insulatinglayer includes a window over said region of opposite conductivity typeand a metal layer overlies a portion of said layer and extends into saidwindow to form ohmic contact with said region.
 4. A semiconductor deviceincluding a silicon substrate of one conductivity type, spaced regionsof opposite conductivity type extending into said substrate and formingjunctions therewith, a protective and insulating layer formed on onesurface of said device and extending over said junctions, said layercomprising a composition of silicon, oxygen and nitrogen (Six Oy Nz) inwhich x 30% to 40% y 45% to 55% z 10% to 20% where x, y and z are Theatomic percentages for silicon, oxygen and nitrogen respectively, spacedopenings formed in said layer over said regions, metal layers extendingover said insulating layer and extending to said regions to make ohmiccontact therewith, and an additional metal layer over the portion of theinsulating layer between said regions, said metal layers forming sourceand drain contacts and said additional metal layer forming the gatecontact of a metal oxide silicon field effect transistor.
 5. Asemiconductor device including a silicon substrate of one conductivitytype, a region of opposite conductivity type extending into saidsubstrate to form a junction therewith, spaced regions of the sameconductivity type extending into said substrate, one of said regionsextending into said region of opposite conductivity type to form ajunction therewith, a protective insulating layer carried on said onesurface extending over said junction to passivate and protect thejunction, said layer comprising a composition of silicon, oxygen andnitrogen (Six Oy Nz) in which x 30% to 40% y 45% to 55% z 10% to 20%where x, y and z are the atomic percentages for silicon, oxygen andnitrogen respectively, openings formed in said layer to expose saidregion of opposite conductivity type and said spaced regions of the sameconductivity type, a metal layer having individual portions extendinginto said openings to contact said regions and carried by the insulatinglayer, said individual portions defining emitter, base and collectorcontacts.